Problem with integral derailleur lines

So let me start by saying that the bike frame is an older version of an Apex Soniq. It was made around 2015-16 I believe. I'm building it up with a Sram Force 22 groupset. The way they did the cable routing is a bit bizzare for me. There's no space for the cable housing inside the frame, you just have to thread in the line itself. The problem is that the line is going through very badly. I had to push it through using a lot of force because it somehow got stuck midway. Now the line is through but the rear derailleur isn't shifting properly no matter the setup. I noticed that the line isn't coming back/loosening easily. Am I missing something? I tried lubing up the line itself, also spraying something inside the routing. There's also no inspection hole around the bottom bracket so I have no way of seeing what's going on.